1. Field of the Invention
This invention relates to bone-derived implants, or osteoimplants, made up of a coherent aggregate of elongate bone particles and to methods for their manufacture. Among their many applications, the osteoimplants herein can be fashioned in various configurations and sizes for use in repairing bone defects, e.g., as strips for use in spinal fusion procedures, as trough-shaped implants especially useful for PostLateral Fusion (“PLF”) procedures, and as putty-like materials that can be molded on site and packed between fragments of bone fractures, between bony projections and into large cavities.
2. Description of the Related Art
Bone-derived implants have been used extensively to treat various medical problems in human and animal orthopedic surgical practice. The use of such implants has also extended to the fields of, e.g., cosmetic and reconstructive surgery, dental reconstructive surgery, podiatry, orthopaedics, neurosurgery and other medical fields involving hard tissue. The use of autograft bone (where the patient provides the source), allograft bone (where another individual of the same species provides the source) or xenograft bone (where another individual of a different species provides the source) is well known in both human and veterinary medicine. In particular, transplanted bone is known to provide support, promote healing, fill bony cavities, separate bony elements (such as vertebral bodies), promote fusion (where bones are induced to grow together into a single, solid unit) or stabilize the sites of fractures. More recently, processed bone has been developed into shapes for use in new surgical applications or as new materials for implants that were historically based on non-biologically derived materials.
Osteoconductive materials are ones that guide bone growth but do not stimulate it. Examples are bone chips and ceramics. Osteoinductive materials actually cause bone to form and result in faster and more certain healing. Examples of osteoinductive materials include cancellous bone, demineralized bone and various growth factors. The most common source of osteoinductive material is the patient's own bone. Typically, in spinal surgery, this is harvested from the iliac crest in the form of bone chips and marrow. While effective, it causes secondary damage (to the harvest site) and requires preparation before it can be used. Furthermore, it is somewhat difficult to maintain in place due to its semi-fluid nature.
Demineralized bone is an alternative to bone chips and marrow as an osteoinductive material. Compositions containing demineralized bone come in various forms including gels, pastes, fibers, sheets, and the like. The more fluid compositions such as those made with bone powder are relatively easy to implant at the repair site but difficult to maintain in place. Osteoimplants made with elongate bone particles, in contrast to those made from bone powder, are better able to maintain their implanted shape and mass and to resist or delay erosion by body fluids and irrigation liquids. Elongate bone particles and methods for their manufacture are described in, inter alia, U.S. Pat. Nos. 5,314,476, 5,507,813, 5,607,269 and 6,436,138, in pending U.S. patent application Ser. No. 10/137,862, filed May 2, 2002 and WO 03/082159.